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    20 May 2022 Volume 41 Issue 5
      
    My academic relationship with the journal College Physics
    SUN Chang-pu
    College Physics. 2022, 41(5):  1.  doi:10.16854/j.cnki.1000-0712.210610
    Abstract ( 90 )   PDF (336KB) ( 48 )  
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    College Physics is an important professional journal for physics teaching and education in China. For me, it is a platform for starting my scientific research. Two papers were published in College Physics during my college years, which not only affected my research style and scientific taste, but also strengthened my confidence in the path of scientific research. My personal growth experience shows that running a professional teaching journal, such as College Physics, can help young people realize the leap from learning knowledge to creating knowledge
    Teaching the photoelectric effect in a time-resolved perspective
    HE Feng
    College Physics. 2022, 41(5):  6.  doi:10.16854/j.cnki.1000-0712.210300
    Abstract ( 94 )   PDF (243KB) ( 57 )  
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    The photoelectric effect is fundamental in laser-matter interaction. Generally, students are taught by introducing the Einstein’s photoelectric-effect equation. In this paper, we propose to teach the photoelectric effect in a time-resolved perspective. According to the time-dependent perturbation theory, the electron may absorb random photons at any time, and the transitions at different moments interfere each other, resulting in the ultimate photoelectron within the expectation of Einstein’s photoelectric-effect equation. The similarity about the time-resolved photoelectric effect and Feynman path integral is analyzed. Students are suggested to conceive a strategy to observed the double-time-slit interference by using two laser pulses. 
    Research on forced vibration of strings under point driving force
    WANG Yi-ming, SONG Rui, LIU Ji-chen, SUN Di-jia
    College Physics. 2022, 41(5):  9.  doi:10.16854/j.cnki.1000-0712.210337
    Abstract ( 62 )   PDF (301KB) ( 41 )  
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    In this paper,the equation of forced vibration of the undamping strings driven by a periodic driving force was established by means of Dirac δ function. The equation is solved with boundary conditions. The solution is shown and the influence of frequency on amplitude was analyzed. Resonance, antiresonance and pseudoresonance were found, and the conditions of the three phenomenons are determined. At last, the experiments on verifying the conditions of resonance and pseudoresonance are designed, the experiment results are consistent with theoretical predictions.
    Dispersion relation of one dimensional j-atom chain lattice vibration
    ZHENG Shi-yan, YUAN Yi-pu, CHANG Dou-liang
    College Physics. 2022, 41(5):  13.  doi:10.16854/j.cnki.1000-0712.210340
    Abstract ( 59 )   PDF (454KB) ( 44 )  
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    In this paper, lattice vibration of one-dimensional j-atom chain is taken as the theoretical calculation model, and its equations are obtained under the harmonic and the nearest adjacent approximation. By setting j=1, 2, and 3, respectively, the dispersion relations of one-dimensional single atom, two atoms and three atoms chain lattice vibration are derived which are the same as those in the existing textbooks and references. The results have shown that the equations of one-dimensional j-atom chain lattice vibration obtained in this paper are general. Then starting from this set of equations, the influence of typical crystal structure parameters (such as atomic distance, restoring force coefficient, and atomic mass) on the dispersion relations of one-dimensional four atoms chain lattice vibration is analyzed by numerical simulation, which intensifies the impact of related content of lattice vibration in solid-state physics, and provides a certain reference value for the fabrication of band-pass filters in engineering.
    Derivation of relativistic transformations of electromagnetic fields via the full Maxwell equations
    HUANG Yong-yi
    College Physics. 2022, 41(5):  19.  doi:10.16854/j.cnki.1000-0712.210390
    Abstract ( 57 )   PDF (179KB) ( 67 )  
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    Via the full Maxwell equations and relativity principle, we straightforward derive relativistic transformations of electric field intensity, magnetic induction intensity, electric displacement vector, magnetic field intensity, volume charge density and current density vector.
    Solving the motion of free photons in black hole background via Lagrangian
    WEI Shao-wen, FU Chun-e
    College Physics. 2022, 41(5):  23.  doi:10.16854/j.cnki.1000-0712.210416
    Abstract ( 47 )   PDF (231KB) ( 51 )  
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    Solving mechanical problems with Lagrangian is a very useful method. In this paper, the motion of free photons in the background of a black hole is solved by means of Lagrangian. After obtaining the four velocities of photons, the allowable motion range of photons with different energies is studied by means of the law of conservation of mechanical energy. Then, according to the inverse problem of kinematics in mechanics, the trajectory of photons is finally obtained.
    The concept and nature of light
    GE Bao-an
    College Physics. 2022, 41(5):  25.  doi:10.16854/j.cnki.1000-0712.210406
    Abstract ( 71 )   PDF (173KB) ( 68 )  
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    Light is one of the first benefits humans felt from the universe. Optics is one of the oldest branches of physics. One of the biggest challenges to understanding the nature of light is whether it follows the principle of entropy increase. 
    Phenomenon and analysis of ruler diffraction
    JIANG Xiang-qian, WANG Ying, SONG Yang, ZHAO Chun-yu, ZHANG Yu
    College Physics. 2022, 41(5):  27.  doi:10.16854/j.cnki.1000-0712.210459
    Abstract ( 44 )   PDF (237KB) ( 36 )  
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    Diffraction is an important characteristics of the wave aspect of light, and grating diffraction is an important phenomenon of diffraction. A hemicycle diffraction speckle is found when a light irradiates the edge or the surface of a ruler, however, the mechanism of this phenomenon is still not clear. In this paper, combing theoretical and experimental methods we study the mechanism of the hemicycle diffracted speckle. It is found that the diffracted speckle is hemicycle when the gratinglike structure exists in the edge or the surface of a ruler. Using the standard binary grating model we analyze the diffraction of rulers, and found that the hemicycle diffracted speckle originates from the superposition of multigrating diffraction.
    Practice of optical device design and research training of student 
    WANG Hui-qin
    College Physics. 2022, 41(5):  30.  doi:10.16854/j.cnki.1000-0712.210405
    Abstract ( 32 )   PDF (333KB) ( 18 )  
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     Research training based on optical device design has been carried out in this paper. The practice of teaching and research integration has been implemented by revolving knowledge, ability and quality on the undergraduates for cultivating their innovative ability. Training progress has been carried out by means of literature research, design practice, sharing discussion, and group reply systematically. Teaching activities have been organized in the form of sharing report and discussing weekly. After a year of training, students have not only deeply internalized their professional knowledge, but also improved their practical ability, expression ability, innovation ability and hard-working spirit.
    Einstein and PlanckIn commemoration of the 100th anniversary of the photoelectric effect award
    ZHANG Yan, YANG Qing-yu
    College Physics. 2022, 41(5):  35.  doi:10.16854/j.cnki.1000-0712.210277
    Abstract ( 44 )   PDF (214KB) ( 21 )  
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     Einstein is a legend in the history of physics in the 20th century. 1905 was a milestone for him, and his five consecutive papers became the first peak of his scientific career. One of them, entitled “an enlightening view on the generation and transformation of light”, he won the Nobel Prize in physics in 1921. Planck appreciated Einstein’s talent very much. Helbron commented: “Planck’s second most important discovery is Einstein”.
    “Measure and object to reason, deliberate thinking and earnest action”— teaching  reform, innovation and practice of mathematics and physics method course
    ZHU Jun, LI Lu, LI Zhi-jian, MA Jie
    College Physics. 2022, 41(5):  41.  doi:10.16854/j.cnki.1000-0712.210431
    Abstract ( 42 )   PDF (292KB) ( 16 )  
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     The team of mathematics and physics method course in Shanxi university tried to reform and innovate all aspects of teaching. Teaching idea was innovated to achieve the goal of cultivating innovative and top physics talents. The teaching content was improved to reflect the function of connecting the preceding to the following and reorganized to meet the great demand of national research on quantum science and technology. The teaching mode was innovated to realize the student-centered teaching and the mutual integration of mathematics and physics. Objective and effective teaching evaluation ensured the teaching quality and improved teaching effect. Through ideological and political education, ‘spring breeze and rain, moisten things silently’ was realized.
    Using PASCO system to study the vibration of  two-degree freedom system under resistance 
    ZHAO Zi-yuan, ZHAO Kang-xin, LANG Chi-cheng, KANG Xiu-ying
    College Physics. 2022, 41(5):  47.  doi:10.16854/j.cnki.1000-0712.210506
    Abstract ( 34 )   PDF (847KB) ( 23 )  
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    In this paper the vibration of two-degree freedom system was explored in theoretic and experimental way, and a set of motion equations was given by considering the influence of friction and air resistance. Three springs and two position sensors were used to build an experimental device. The PASCO system was used for experiments which were compared with the numerical simulation results. The friction forces of the two sensor sliders in this system were obtained as 0.003 075 N and 0.003 225 N, and the air resistance coefficient was C=1.0. The accuracy of the modelling of the studied system was also verified. The experimental results have a certain reference value for the study of vibration problem of two-degree freedom system.
    A method of measurement of local gravitational acceleration based on single  pendulum combined with electromagnetic induction principle
    WEI Jie, YI Jia-le, YU Hui-qin, YANG Fan, TIAN Yong, HE Xiao-feng, LI Lin, HU Xiao-jun
    College Physics. 2022, 41(5):  52.  doi:10.16854/j.cnki.1000-0712.210435
    Abstract ( 49 )   PDF (265KB) ( 35 )  
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    In this paper, single pendulum method is combined with electromagnetic induction principle in the experiments. A permanent magnetic sphere as the pendulum ball is used and a multiturn coil is placed directly under it. When the pendulum ball moves in simple harmonic motion, magnetic flux in the coil is disturbed and thereby a periodic induced electromotive force is generated. A filter module was used to suppress the noise and the electromotive force signal was collected by an oscilloscope. As a result, the pendulum period could be determined accurately by collecting electromotive force signal. Furthermore, the distance between the coil and pendulum ball was changed in order to evaluate the effect of electromagnetic damping. The measurement was repeated at different distance and the measured period data was found to be independent on the distance configurations. It indicated that electromagnetic damping could be ignored which was in agreement with our semiquantitative analysis. The local gravitational acceleration measured in this paper was good consistent with the reference value.
    Self-diffusion and electrofreezing of bulk water under electric field
    GUAN Xing-yue, LI Wen-fei
    College Physics. 2022, 41(5):  63.  doi:10.16854/j.cnki.1000-0712.210480
    Abstract ( 41 )   PDF (458KB) ( 24 )  
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    Diffusion and phase transition are important elements of basic physics teaching at the undergraduate level. In this paper, we study the diffusion and phase transition of water molecules under an external uniform electric field based on molecular dynamics simulations for bulk water system. In the case of smaller electric field, water molecules exhibit significant angular jump reorientation motions, and the frequency of the rotation shows a non-monotonic increasing-decreasing behavior with the electric field. This anomalous electric field dependence of angular jump reorientation is strongly correlated with the non-monotonicity of the diffusion coefficient of water molecules with electric field. The liquid-solid phase transition of the bulk water system, i.e., electrofreezing phenomenon, was reproduced at stronger electric fields, and the layered stacking pattern of the two ice phases was observed. The direction of this layered stacking pattern is consistent with the direction of the electric field. The molecular simulations provide new insights into the molecular mechanisms of water diffusion and phase transition at the microscopic level, and can be used as a teaching example for students to develop research interests and research practice skills.
    Transmission dynamics of COVID-19 in calm air
    OU Zhong-wen, LIU Jun-bing, WANG Yue-ming
    College Physics. 2022, 41(5):  63.  doi:10.16854/j.cnki.1000-0712.210386
    Abstract ( 35 )   PDF (446KB) ( 34 )  
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     Based on the main existing form of viral in the air being attached to tiny droplets from normal breathing or coughing and sneezing, we mainly consider those droplets’ temporal and space dynamics with radius of 0.05~100μm in calm air. It is found that the drops with radiuses are close to 100μm stay in the air less than 2 seconds, which can carry the virus away up to 0.61m when one cough or sneeze. When the radius is in the range of 1~10μm the floating droplets carrying with virus can survive 3.7 hours in the air. While the droplet’s dimension is close to the viral’s it will be present in calm air for nearly one month, and will also have significant diffusions in the air.
    Using capacitance-voltage method to study the structural characteristics of  GaN-based double heterojunction light emitting diodes
    FAN Qian-qian, XU Kun-yi, FU Si-lie
    College Physics. 2022, 41(5):  69.  doi:10.16854/j.cnki.1000-0712.210457
    Abstract ( 29 )   PDF (389KB) ( 19 )  
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    In this paper, the double heterojunction structure of GaN based blue light emitting diodes is studied by capacitance voltage method (C-V method). The C-V curve of the measured samples is divided into two parts from the change center, and the PN junction types are analyzed respectively. Then, the temperature of the diodes is controlled by liquid nitrogen, the C-V curves at different temperatures and the corresponding impurity concentration distribution curves are obtained, and the influence of temperature on them is analyzed. Finally, the double heterostructure of GaN based blue light emitting diodes is analyzed from the impurity concentration distribution curves at different temperatures. The experimental results have showed that the PN junction type of GaN based double heterojunction blue light diode is abrupt junction on both sides; At different temperatures, the capacitance of the sample increases with the increase of temperature and decreased with the decrease of temperature. The double heterostructure is gradually significant with the decrease of temperature. When T= 98 K, the double heterostructure tends to be ideal.
    Explanations of abnormal phenomena in the measurement of sound  velocity in water based on Gaussian beam model
    WANG Ke-xin, ZHOU Shi-yun
    College Physics. 2022, 41(5):  74.  doi:10.16854 /j.cnki.1000-0712.210347
    Abstract ( 29 )   PDF (357KB) ( 16 )  
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    In the measurement of sound velocity in water,abnormal phenomenon appears that the magnitude of locally maximum of sound pressure on the receiving transducer increases as the receiver moves away from the emission transducer,which differs from the prediction of ideal model and conflicts with the common sense of attenuation in water.Furthermore,the relationship of the locally maximum pressure and the distance between two transducers depends on the height of water in the tank.To solve the myth above,the superposition of Gaussian beams and the method of image sources are applied.Equipped with the analytic expression of the relationship between the pressure and the distance,numerical simulation reproduces the non-monotonic decreasing as seen in the experiment,thus the speculation that the reflection on the interface of water-air and water-tank contributed to such phenomena is verified.
    Probe into the performance of soap membrane filter
    MA Zhou-yang, GUAN Zhou, ZHAO Shu-min, FANG Ai-ping, ZHAO Di
    College Physics. 2022, 41(5):  80.  doi:10.16854 /j.cnki.1000-0712.210489
    Abstract ( 31 )   PDF (364KB) ( 26 )  
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    Material separation is the core technology of many medical and industrial applications.Traditional solid filtration membranes can allow particles smaller than the critical size to pass through the membrane while blocking the passage of larger particles.However,membranes that allow large particles to pass through while small particles stay are difficult to make artificially.Stogin,Gockowski,et al (in Sci.Adv.2018,4:3276) proved that a liquid membrane composed entirely of liquid can be designed to retain particles smaller than the critical size and permeate largesize particles.Based on the above research,this article analyzes and derives based on the liquid membrane filter model,analyzes and discusses the critical permeability conditions of the liquid membrane,and is verified in the experiment.At the same time,this article realizes the screening of particle velocity by adjusting the surface tension coefficient of the liquid membrane.